The present invention relates to a seat belt retractor and particularly to a rewind spring for such a retractor and a method for assembling a rewind spring.
In general, a seat belt system has a seat belt retractor. The seat belt retractor has a webbing spool for winding up the seat belt webbing. The webbing spool is constantly biased in the direction for winding up the webbing by a relatively small biasing force. The biasing force prevents the webbing from protracting without the application of a relatively small pulling force. Thus, tension is always applied to the webbing of the seat belt.
A rewind spring in a retractor serves to keep tension on the seat belt webbing by biasing the rotatable spool on which the webbing is wound in a webbing retracted direction. The rewind spring is traditionally in the form of a metal band, preferably a steel band, fixed at one end to an arbor at the axis of the spool and secured at its other end to a fixing point on the spring housing. The band is generally of the form used for clock springs. The band is inserted into the housing by a reverse winding process to provide the requisite tension.
A method of assembling a rewind spring into a retractor currently entails several process steps. In general a coiled metal band is mounted on an unwinding post on a purpose built jig and the end of the band is placed on the winding shaft. A winding apparatus is then lowered over the jig to reverse wind the band onto the jig. When the band is fully reverse wound then the winding apparatus is lifted and a plastic retractor mechanism cover is inserted over and fitted to the reverse wound band. The mechanism cover is then attached to a spring cover, a spring arbor is fixed to the spring and the spring is wound up to tension the spool in the webbing retracted direction. Obviously this is generally lengthy and thus expensive procedure. It is desirable to reduce the number of production steps so as to decrease time and costs.
UK Patent Application 2076635 A teaches an apparatus a seat belt retractor spring assembly, which includes a casing, a shaft, and a spiral spring. This patent application does not teach or suggest a simpler method for assembling a rewind spring in a cassette.
U.S. Pat. No. 4,995,567 teaches an apparatus for a spiral spring of a retractor comprising a male and female complementary elements which are intended to be engaged with one another and the male elements are fragile and are intended to break as a result of the action exerted upon the hub through the orifice, once the spring has been tensioned. This patent does not teach or suggest a simpler method for assembling a rewind spring in a cassette.
UK Patent Application 2265076 A teaches a device for maintaining a biasing force during assembly of a seat belt retractor. This patent does not teach or suggest a simpler method for assembling a rewind spring.
According to one aspect of the present invention there is provided a method of assembling a rewind spring in a cassette for a seat belt retractor, the method comprising: taking a coiled metal band, placing the band on an unwinding post on a jig, placing a mechanism housing on the jig at a position spaced from the unwinding post, fixing one end of the band to a spring arbor, using a winding machine to reverse wind the band onto the arbor, fitting a spring cover to the mechanism cover, and attaching a locking clip to the spring cover to lock the arbor against rotation.
According to a second aspect of the invention there is provided a spring arbor for use in the method of the first aspect, the arbor having a generally cylindrical shape and an axially extending slot for receiving an end of the spring, wherein a step is provided in the profile of the cylindrical outer surface of the arbor in the region of the slot to compensate for the thickness of the band being wound thereon and thereby to prevent interleaf gaps between successive turns of the spring band.
Preferably the step is of a height corresponding to the thickness of the band. In a preferred embodiment the arbor has a hole extending at least partly, and preferably fully, through its axis. This hole locates the arbor on the rewinding apparatus used in the method of the first aspect of the invention. It is advantageously shaped with a non-circular profile, for example with a hexagonal profile or another suitable torx transferring shape.
According to a third aspect of the invention there is provided a locking clip for locking the spring arbor against rotation, and particularly against rotation relative to the spring cover, the clip comprising a pin having an outer profile complimentary to the inner profile of the arbor.
The clip is preferably removable and reusable. Thus additional costs are saved. It is advantageously attached to a transversely extending member with fixing means, preferably at each end, to attach the clip to the spring cover. A tab is preferably provided for levering the clip out of engagement with the cover and the spring arbor when it is desired to remove it.
In a particularly advantageous development the clip has a different color or a distinctive marking so that it is easily recognizable by a machine operator or technician and so that it is easily noted that it is in place, and thus that the spring is pre-wound. For example the clip could be formed of brightly colored plastics material.